To fabricate a product from a sheet material, oftentimes a sheet machine center comes into play. Such machine center may be comprised of a turret punch, a right angle cutter, a laser cutter, or other machines for fabricating components out of a sheet of material, which may be metal, plastic, wood, etc.
Prior to the onset of automatic loader/unloader units that, together with the actual sheet working machine, form a machine center, each workpiece has to be manually loaded onto a work area of the sheet working machine. With an automatic loader, each sheet of material is usually picked up by a number of suction cups, attached to a carriage frame, and fed to the work area of the sheet working machine. Such automatic loader and unloader devices are well known, and are exemplified by, for example, the loader and unloader of the Finn-Power FMM2500, FMM3000, etc. machine centers.
In brief, to load a worksheet to the work area of the sheet working machine, the sheet is first picked up from a stack of sheets, from a so called de-stacker, by a number of suction cups attached to a carriage, which is movable vertically and horizontally. Thereafter, the carriage transfers the picked-up sheet from the de-stacker position to a position above the work area of the sheet working machine and deposits the sheet thereon. Thus, to transport a worksheet from the de-stacker, or the loading table where the sheets are placed, to the work area of the machine, the carriage first has to be lowered until its suction cups make contact with the worksheet on top of the stack. A suction force is next provided to the suction cups for securing the top sheet. Thereafter, the carriage is raised and moved horizontally from the loading table to the work area of the sheet working machine. The carriage is then lowered and the suction force removed from the suction cups to thereby deposit the worksheet onto the work area of the machine.
During the lifting of the top sheet from the stack of sheets, there commonly occurs a situation where the underlying sheet(s) would adhere to the top sheet, due to an under pressure of vacuum condition that may develop between adjacent stacked sheets. The adherence condition is further aggravated if, for example, a fluid such as lubricant or preservative is applied to the sheets prior to stacking. Thus, instead of lifting only the top sheet, the carriage, during the loading operation, may actually pick up some additional underlying sheet(s).
There are a number of ways prior art loading systems attempt to reduce the incidence of more than one sheet being lifted by a carriage during the loading process. Among those are the well known use of fanning magnets which tend to exert a magnetic force on the underlying sheets, if the worksheets are ferrous, so as to prevent them from being picked up at the same time as the top sheet. However, such fanning magnets do not work on nonferrous materials such as, for example, aluminum, plastic, etc.
Another attempt of separating the top sheet from the underlying sheets is disclosed in Jelinek et al. U.S. Pat. No. 4,703,925. There, a group of the suction cups (of the three groups disclosed in the embodiments) is caused to oscillate relative to the other groups so that shear forces are created between the suctioned top sheet and the underlying sheets to thereby cause the underlying sheets to be separated from the top sheet and fall back into the stack of sheets. It is further disclosed in '925 that a vertically oriented flattened fan-shaped blast of air may be directed to the side of the top sheet, to flow both above and below the top sheet, as the top sheet is being lifted by the suction cups. The '925 method works as long as the nozzle for providing the air blast is aligned correctly to the edge of the top sheet and there is a gap effected between the top sheet and its underlying sheets at the moment that the being lifted sheet(s) is/are passing by the air blast. Unfortunately, such is often not the case, as for example in the situation where a gap is not produced between the top sheet and its underlying sheet until after the lifted sheets are well beyond the blast of air from the nozzle. So, too, are there situations where the nozzle is aligned incorrectly so that its air blast is directed somewhere else. Moreover, due to the fact that the air nozzle of the '925 system is located some distance away from the edge of the top sheet, a substantial amount of the air output from the air nozzle is wasted.